Process fluid or gas bearings are now being utilized in an increasing number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween filled with a fluid such as air, which, under dynamic conditions, form a supporting wedge sufficient to prevent contact between the two relatively movable elements.
Improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively movable bearing elements. Such foils, which are generally thin sheets of a compliant material, are deflected by the hydrodynamic film forces between adjacent bearing surfaces and the foils thus enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect.
The ready availability of relatively clean process fluid or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid film lubricated bearings particularly attractive for high speed rotating machinery. While in many cases the hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary to externally pressurize the fluid between the bearing surfaces to increase the load carrying capability. While these externally pressurized or hydrostatic fluid bearings do increase the load carrying capacity, they also introduce the requirement for an external source of clean fluid under pressure.
In order to properly position the compliant foils between the relatively movable bearing elements a number of mounting means have been devised. In thrust bearings, it is conventional practice to mount a plurality of individually spaced foils on a foil bearing disk such as by spot welds and position the foil bearing disk on one of the bearing elements as exemplified in U.S. Pat. No. 3,635,534.
More recently, a thrust bearing disk having integral compliant foil pads which eliminated the need for the plurality of individual foils which had to be individually attached to the thrust bearing disk has been developed and is exemplified in U.S. Pat. No. 4,624,583. This patent has a common inventor with the present application and is herein incorporated by reference.
Two problems associated with the thrust bearing disks of the 4,624,583 patent have been identified. First, fluttering of the individual foils under operating conditions has resulted in the leading edge of the foils moving into contact with the thrust runner, causing wear and premature failure of the thrust bearing disk. Second, since the pressure which is developed between the rotating thrust runner and stationary thrust bearing is zero at the radially outer edge of the foil elements or thrust runner, surface contact and wear occurs and gradually wears through the thrust bearing disk.